1. Field of the Invention
This invention relates in general to methods and devices for make up or joining of a drill string and, more particularly, to methods and devices for applying torque or a regulated torque in such drill string make up.
2. Description of the Prior Art
In rotary drilling it is necessary to join multiple joints or pieces of a drill pipe or rod as the drilling process proceeds. This process is generally known as drill string make up. It occurs repeatedly as the depth of the drilled hole increases or when the drill string is reassembled after it has been removed from the drilled hole.
Generally drill string make up is accomplished by clamping rotary table jaws to a lower section of pipe and then threading an upper section of pipe to the fixed lower section of pipe. The threading is achieved by connecting a wrench-like device called a tong to the upper section of pipe so that the tong arm extends radially from the pipe with the pipe fixed thereto so that as the tong arm rotates the pipe must rotate. In order to supply sufficient force to the tong arm, a winch and winch line are connected to the tong arm and the winch operated until sufficient torque is applied to the upper drill pipe section to provide a secure rotary shoulder connection between the upper pipe joint and the lower pipe joint. Following make up, the tong arm is released and the drill string lowered until an additional pipe joint may be connected to the drill string. Occasionally a pair of opposing tongs are used instead of relying on the rotary table to hold the lower section of pipe.
A particular problem with the make up process in the past has been that the torque applied to the rotary shoulder connection is both unknown and not precise. This results in a connection which is either too loose allowing foreign matter to produce galls during drilling process or too tight damaging the pins or boxes of the connection.
Various attempts have been made to solve this problem of imprecise torque. However, these methods and devices have not proved satisfactory.